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STABILITY AND CHANGE IN THE ASGS
This 2016 edition of the Australian Statistical Geography Standard (ASGS) is the first update to the original edition released in 2011. This chapter describes the degree and manner in which the Main Structure regions have changed in the five years since they were first released, as well as outlining other significant updates incorporated into the 2016 edition of the ASGS.
2016 ASGS STRUCTURES - SIGNIFICANT CHANGES
Significant changes introduced with the 2016 edition include the addition of a boundary and code for Australia, as well as the incorporation of Norfolk Island into the ASGS. The Non ABS structures are now primarily approximated using Mesh Blocks and this means that the boundaries for State Suburbs, Postal Areas, Natural Resource Management Regions and Australian Drainage Divisions are all approximated far more accurately than they were in 2011.
IMPROVED STABILITY FOR ASGS STATISTICAL AREAS
Separating the ABS defined statistical areas from other administrative areas, particularly Local Government Areas, was a key difference in the design of the ASGS compared to the previous Australian Standard Geographical Classification (ASGC). This was done to reduce the impact of Local Government Area changes on ABS designed statistical areas, allowing them to better meet the requirements of statistical datasets and have greater stability for improved comparison of statistical data over time.
Changes to the boundaries of ABS defined areas in the ASGS are still required to reflect changes occurring on the ground, such as new housing developments or transport infrastructure. However, these changes are carefully balanced against the strong desire to maintain stability and continuity with the previous versions of the ASGS. As a result of these changes there have been increases in the number of areas included in all the structures from Mesh Blocks up to Statistical Areas Level 4 (SA4s) as shown in the table below.
Table 1: Change in numbers of Statistical Areas of ASGS Main Structure from 2011 to 2016
The amount of change to the ASGS Main Structure statistical areas is small in comparison to the change that occurred in previous editions of the ASGC and this was a key reason for the implementation of the ASGS. This increased stability of statistical areas in the ASGS allows better comparison of data over time.
Increased stability in the ASGS is illustrated by Figure 1 below showing the percentage of Main Structure statistical areas and Mesh Blocks that have remained effectively unchanged between 2011 and 2016. This level of change has been measured using the 2011 to 2016 population based geographic correspondences, it does not take into account changes that impact area with no population. The larger the region the less likely it is to change as it is better able to absorb changes in population while staying within the defined criteria. The stability of the ASGS is highlighted by comparison with the Local Government Areas. Between 2011 and 2016, 9.5% of Local Government Areas changed, this is more than twice the level of change when compared to similarly sized ASGS Main Structure areas such as SA2s (4.5% change) and SA3s (3.1% change).
Figure 1: Percentage of 2011 ASGS Statistical Areas remaining effectively unchanged in the 2016 ASGS
REASONS FOR CHANGE IN ASGS STATISTICAL AREAS
Although stability in the ABS defined statistical areas is important, it is also necessary to change some areas to continue to meet the requirements of the statistical data that is published on them or to better reflect the changing settlement patterns they represent. These changes can occur in three main ways; splits, amalgamations and redesign. The nature and extent of these changes for the main structure is shown in the chart below.
Figure 2: Types of change to ASGS Main Structure Areas (Percentage of 2011 Areas changed)
Figure 3: Image showing an example of SA1 splits to reflect growth
Figure 4: Image showing an example of SA2 amalgamations to meet statistical criteria
Figure 5: Image showing an example of Mesh Block amalgamations
Figure 6: Images showing an example of boundary redesign to account for new growth
CHANGES TO ASGS CODES
ASGS users should be aware that the codes and names that are associated with statistical areas can also change when an area changes. In addition, where changes occur in the larger Statistical Area regions this can result in changes to the code for the smaller areas contained within them, even if one of these smaller areas has not changed itself. This occurs because the ABS Structures within the ASGS have a hierarchical coding system, meaning the smaller areas carry the codes associated with the larger areas. For example an SA2 may not have changed but if it is within an SA3 that has changed, then both the SA3 and SA2 code will have changed along with all other SA2 and SA1 codes within that SA3.
For more information on ASGS code changes please refer to Appendix 2: ASGS Coding and Labelling Changes.
UNDERSTANDING CHANGE IN THE ASGS
The ABS provides several resources to help users understand these changes to boundaries and codes and to manage data across different ASGS editions and other geographies.
Geographic correspondences document the overlaps between two sets of regions. They provide a percentage for data allocation between the overlaps that are based on estimates of the population distribution with the two regions. Geographic correspondences between 2011 and 2016 editions of statistical areas are available in the downloads tab of the relevant ASGS publication. These can be used to understand the relationships between 2011 and 2016 areas and to convert data from 2011 ASGS regions to 2016 regions.
ABS Maps is an online mapping tool that allows users to visually compare two different sets of boundaries across different editions of the ASGS. This allows users to examine the nature and extent of individual boundary changes in their area of interest.
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